In recent years, the development of various types of electrical instruments such as wristwatches, calculators, computers, etc., which operate electronically, has generated a need for digital display devices. Where the instruments are to be portable, and therefore separated from powered mains, it is highly desirable that the digital display device should consume as little power as possible. As digital devices, display cells using liquid crystals, light-emitting diodes and the electrochromic effect have been devised. So far as the liquid crystals are concerned, the display cannot be seen clearly where the light level is low, so that the color tones developed are indistinct and the contrast is low. As for light-emitting diodes, the consumption of power is substantial so that, so far as a wristwatch is concerned, it becomes necessary to provide for push-button actuation, a serious inconvenience requiring the use of both hands. As for the electrochromic devices, an extremely clear display can be obtained at a low power level, but displays of this type have not come into wide use because of the following defects:
1. The useful life of the electrode is short. PA0 2. It is difficult to erase the display, once the need for same is terminated. PA0 3. The response speed is inadequate for many uses. PA0 4. Display arrangements used thus far have been rendered confusing due to the fact that the conductive leads become visible. PA0 5. The operating voltage required to activate the display is substantially above that which causes electrolysis of water which must be present. This leads to degradation of the system and a short operating life.
As is evident, electrochromic display cells would have much wider application than at present if the above difficulties could be eliminated.